CA2000256A1

CA2000256A1 - Method of making a color filter array element using a heated embossed surface

Info

Publication number: CA2000256A1
Application number: CA002000256A
Authority: CA
Inventors: Michael J. Simons
Original assignee: Individual
Current assignee: Eastman Kodak Co
Priority date: 1988-10-18
Filing date: 1989-10-06
Publication date: 1990-04-18
Also published as: ATE116449T1; US4978652A; GB8824365D0; EP0365219A2; DE68920266T2; JP2714456B2; EP0365219B1; DE68920266D1; JPH02176707A; EP0365219A3

Abstract

METHOD OF MAKING A COLOR FILTER ARRAY
ELEMENT USING A HEATED EMBOSSED SURFACE
Abstract of the Disclosure A method of making an array of a repeating mosaic pattern of colorants carried on a support using (a) a plurality of donor materials each comprising respectively a sublimable dye of a different color, and (b) a receiver element comprising a support having thereon a dye-receiving layer, wherein each donor material is in turn brought into face-to-face contact with the receiver and heated patternwise by contact with a heated embossed surface to transfer the desired pattern of dye to the dye-receiving layer.

Description

- ~t~

METHOD OF MAKING A COLOR FILTER ARRAY
ELEMENT USlNG A ~ATED EMBOSSED SU~FACE
This invention relate~ to a method of making a color filter array ~lement by therma~ tran~er.
In recent years, thermal trans~er 8y8tem3 have been developed to obtain pri~tB ~rom pictures which have been generated electronically from a color video camera. According to one way of obtaining such prlnts, an electronic picture i8 first subjected to color separation by color fi~ters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain thc print, a cyan, magenta or yellow dye-donor element ie placed face-to-face ~ith a dye-receiving element. The two are then inserted bet~een a thermal printing head and a platen roller. A line-type thermal printing head is u~ed to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process i9 then repeated for the other two color~. A color hard copy is thus obtained which corresponds to the original picture viewed on a ~creen. Further details of this process and an apparatus for carrying it out are contained in U.S. Patent No. 4,621,271 by Brownstein entitled ~Apparatus and Method For Controlling A Thermal Printer Apparatus," issued November 4, 1986.
Liquid crystal display devices are known for digital display in electronic calculators~ clocks, houeehold appliances, audio equipment, etc. There has been a need to incorporate a color dieplay Z~ q. I~r l_P~

capability into ~uch monochrome display device~, particularly in such applications as peripheral terminals using variou~ kinds of equipment involving phototube display, mounted electronic di3play, or TV-image display. Various attempt~ have been made to incorporate a color display using a color ~ilter array element into these device~. However, none of the color array elements for liquid crystal display device~ so far proposed have been successful in meeting all the u~ers needs.
One commercially-available type of color filter array element which has been used in liquid crystal di~play devices for color display capability is a transparent support having a gelatin layer thereon which contains dyes having the additive primary colors red, green and blue in a mosaic pattern obtained by using a photolithographic technique. To prepare ~uch a color filter array element, a gelatin layer is sensitized, expo~ed to a mask for one of the colors of the mo~aic pattern, developed to harden the gelatin in the exposed areas, and washed to remove the unexposed (uncrosslinked) gelatin, thu~ producing a pat~ern of gelatin which is then dyed with dye of the desired color. The element is then recoated and the above steps are repeated to obtain the other two color~. Thi~ method contains many labor-intensive steps, r~quires care~ul alignment, is time-consuming and very costly.
Further detail 8 of this process are disclosed in U.S. Patent 4,081,277.
In addition, a cvlor filter array element to be u~ed in a liquid crystal display device may have to undergo rather ~evere heating and treatment steps during manufacture. For example, a transparent electrode layer, such as indium tin oxide, i~ u~ually vacuum sputtered onto the color filter array `5~

element. Thi~ may take place at temperatures elevated as high a~ 200~C ~or time8 which may be one hour or more. Thi~ is followed by coating with a thin alignment layer for the liquid crystal~, æuch a~
a polyimide. Regardless of the alignment layer used, the ~urface finish of this layer in contact with the liquid crystals is very important and may require rubbing or may require curing for several hour~ at an elevated temperature. These treatment stepæ can be very harmful to many color filter array elements, especially those with a gelatin matrix.
Another method of obtaining a color filter array element for a liquid crystal display device i9 described in EPA 246,334, Thiæ method employs a porous membrane to contain the dyes which are transferred by heat under reduced pressure using a metal mask. There is a problem in that technique in obtaining sufficient sharpness of the image since the dyes have to transfer from the donor layer to the receiver layer through the air gap formed by the thickness of the metal mask.
It would be desirable to provide a method of m~king a high quality color filter array element having good sharpness and ~hich can be obtained easily and at a lower price than tho~e of the prior art.
The~e and other objects are achieved in accordance with this invention which comprises a method of making an array of a repeating mosaic pattern of colorants carried on a ~upport u~ing (a) a plurality of donor materialh each comprising respectively a sublimable dye of a different color, and (b) a receiver element compriæing a ~upport having thereon a dye-receiving layer, wherein each donor material i8 in turn brought into face-to-face contact with the receiver and heated patternwise by contact with a heated embossed surface to transfer the de~ired pattern of dye to the dye-receiving layer.
In a preferred embodiment o~ the invention, the mosaic pattern consists of a set of red, green and blue additive primaries.
In another preferred embodiment of the i~vention, each area of primary color and each set of primary colors are separated rom each other by an opaque area, e.g. black grid lines. This has been found to give improved color reproduction and reduce flare in the displayed image.
The size of the mosaic set is not critical since it depends on the viewing distance. In general, the individual pixels (mosaic element~) of the set are from about 50 to about 600 ~m. They do not have to be of the same size.
In a preferred embodiment of the invention, the repeating mo~aic pattern of dye to form the color filter array element consists of uniform, square, linear repeating areas, with one color diagonal displacement as follows:
~5 &~ ~R G
B ~ G B R
G B ~ G~ \

In another preferred embodiment, the above squares are approximately 100 ~m.
As noted above, the color filter array elemerlts of the invention are used in variou3 display devices such as a liquid crystal display device.
Such liquid crystal display devices are described, for example, in UK Patents 2,154,355; 2,130,781;

2,162,674 and 2,161,971.

211 ~

The heated embossed sur~ace i8 preferably applied to the back of the donor element while it i8 in contact with the receiver element.
The term "embo~sed surface" ~s used herein means a surface having a relief pattern on it~
~urface. While the pattern could be formed by embossing, this is not the preferred method.
Preferably the embo~ed surface may be made of copper or brass to which a layer of photoresi~t haY been applied. The layer is then patternwise expo~ed and developed to provide a patterned resist. The metal sheet is then etched to provide the desired raised pattern. The embossed metal may be mounted on a heatable roller which preferably has a compliant layer immediately underneath the embo~sed layer to ensure better contact with the back of the donor sheet. Alternatively, a vacuum applied through the roller may be used to achieve good contact.
The su~cessive dye donor ~eets may be passed under the same emb~s~ed roller while adjusting the position o~ the laminate to ensure that the dyes are transferred to neighboring areas of ~he receiver, or a set of different embossed rollers may be employed.
The receiver comprises a support and a receiver layer. Such a layer may compri3e a porous ~ilica-containing layer, but pre~erably comprises a polymeric binder.
The polymeric binder employed in the receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polye~ter, a polyvinyl chloride, a polyamide, a polystyrene, a polyacrylonitrile, a poly~caprolactone) or mixtures or copolymer~ thereof. The polymeric binder ~ay be present in any amount which i8 effective ~or the intended purpose. In general, good re~ult~ have been 2~J ~ ?~

obtained at a concenkration of f rom about O . 25 to about 5 g/m2.
In another preferred embodiment, the polymeric binder employed in the r~eeiYing layer i8 cross-linked after transfer of the filter array image. This enables the color filter display to be more resistant to the rather severe heating and etching treatment step~ which are generally necessary in forming a liquid crystal display devic~. Examples of such cros~-linkab~e polymeric binders include polymers which may be cros~-linked by re~ction with another Qubstance pre~ent in or applied to the layer, such as epoxide resins ~reacting with, for e~ample, amines), unæaturated polyestex~ (u~ing, ~or example, organic peroxides), phenolic resins (reacting with, for example, aldehydes), or polyurethanes (reacting with, for example~ di-isocyanates); and polymer systems which may be cross-linked on exposure to light, in the presence of photoinitiators or photosensitizers. Further details of such cross-linkable polymeric binders are found in Application Serial No. of Simons, entitled "Thermally-Transferred Color Filter Array Element,"
filed of even date herewi~h.
The support ~or the color filter array may be any transparent material ~uch aa polycarbonate, polyethylene terephthalate, cellulose acetate, polystyrene, etc. In a preferred embodiment the support is glass.
A dye-donor element that i8 used in the process of the invention to form the color filter array element comprises a ~upport having thereon a dye layer. Any dye or mixture of dyes can be used in æuch a layer provided they are trans~erable to the dye image-receiving layer o~ the color array element of the invention by the action of heat. E~pecially good re~ult8 have been obtained with 8ublimable dyes. Examples of sublimable dyes include anthraquinone dyes, e.g., Sumikalon Violet RSTM
(Sumitomo Chemical Co., Ltd. ), Diani~ Fast Violet 3R-FSTM (Mitsubishi Chemical Industries, Ltd.), and Kayalon Polyol Brilliant Blue N-BGMTM and XST Black 146TM (Nippon Kayaku Co., Ltd. ); azo dyes such as Kayalon Polyol Brilliant Blue BMTM, Kayalon Polyol Dark Blue 2BMTM, and KST Black KRTM (Nippon Kayaku Co., L~d.), Sumickaron Diazo Black 5GTM
(Sumitomo Chemical Co., Ltd.), and Miktazol Black 5GHTM (Mitsui Toatsu Chemicals, Inc.); direct dyes such as Direct Dark Green BTM (Mi~subi~hi Chemical Industries, Ltd.) and Direct Brown MTM and Direct Fast Black DTM (Nippon Kayaku Co. Ltd.); acid dyes such as Kayanol Milling Cyanine 5RTM (Nippon Kayaku Co. Ltd.); basic dyes such as Sumicacryl Blue 6GTM
(Sumitomo Chemical Co., Ltd.), and Aizen Malachite GreenTM (Hodogaya Chemical Co., Ltd.);

CH3~ CN
N~ / -N=N-~ /o-N(C~5)(CH2C6H5) (magenta) NHCOC~3 . 3~,/ 3 N-C H
=CH-CH_s/ I 6 5 (yellow) N(CH3)2 CONHC~3 I 0 0 ~cyan) ~./ \ /
N~ -N(C H ) 2J~'q;~,5~

or any o~ the dye~ di~clos0d in U.S. Patent 4,541,830. The above subtractive dye~ may be employed in various combinations to obtain the desired red, blue and ~reen additive primary colors.
The dyes may be mixed within the dye layer or transferred ~equentially if coated in ~eparat~ dye layers. The dyes may be used at a coverage of from about 0.05 to about l g/m2.
The dye in the dye-donor element is preferably dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulo~e acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate; a polycarbonate;
poly(styrene-co-acrylonitrile), a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from about 0.1 to about 5 g/m2.
The dye layer of the dye-donor element may be coated on the support or printed thereon by a printing technique such a~ a gravure process.
Any material can be used as the ~upport for the dye-donor element provided it i6 dimensionally stable and can withstand the heat of the thermal printing proces~ Such materials include polye~ter~
such as poly~ethylcne terephthalate); polyamide~;
polycarbonatea; glas~ine paper; condenser paper;
cellulose esters; fluorine polymers; polyethers;
polyacetals; polyolefins; and polyimides. The support generally has a thiekness of from about 2 to about 30 ~m. It may also be coated with a subbing layer, if desired.
The dye-donor element employed in the invention may be used in sheet form or in a continuous roll or ribbon.

Zil7 ~ rq~

After the dye~ are transferred to the receiver, the image may be treated to further diffuse the dye into the dye-receiving layer in order stabilize the image. Thi may be done by radiant heating, solvent vapor, or by contact with heated rollers. The fusing step aids in preventing ~ading and surface abrasion of the image upon expo8ure to light and also tends to prevent crystallization of the dyes. Solvent vapor fusing may al30 be used instead of thermal fusing.
The following example is provided to illustrate the invention.

Example A dye-donor of alternating sequential areas of cyan, magenta and yellow dye was prepared by coating on a 6 ~m poly(ethylene terephthalate) support:
1) a subbing layer of a titanium alkoxide (duPont Tyzor TBTTM )(0,12 g/m2) from a n-propyl acetate and n-butyl alcohol solvent mixture, and 2) a dye layer containing the cyan dye illu~trated abo~e (0.28 g/m2), the magenta dye illu~trated above (0.15 g/m~) or the yellow dye illu~trated above (0.14 g/m ), and Micropowder3, Inc. Fluo-~TTM
micronized polytetrafluoroethylene~O.05 glm ), in a cellulose acetate propionate (2.5% acetyl, 45% propionyl) binder (0.25-0.32 g/m2~ coated from a toluene, methanol and cyclopentanone ~olvent mixture.
On the rear of the dye-donor was coated:
1) a subbing layer of a titanium alko~ide (duPont Tyzor TBTTM )(0.12 g/m2) from a n-propyl acetate and n-butyl alcohol solvent mixture, and 2~1~ r~

2) a 81ippi~g layer o~ Petrarch System~
PS513TM amino-terminated polysiloxane (0.001 g/m2); p-toluenesulfonic acid (2.5~/~
of the wt. of th~ polysilo~ane); Emralon 329TM (Acheson Colloids Corp.) dry film lubricant of poly(tetra1uoroethylene~
particles in a cellulose nitrate resin binder (0.54 g/m2); and BYK-3~0TM (BYX
Chemie, USA) copolymer of a polyalkylene lQ oxide and a methyl alkylsiloxane (0.002 g/m2), coated from a n-propyl acetate, tolucne, isopropyl alcohol and n-buty1 alcohol solvent mixture.
An embossed copper roller was made by coating a thin sheet o~ copper with Kodak Micro Resist 747TM photore~i~t, and the excess poured o~
so as to leave a thin film. It wa~ then dried, exposed through a mask of the desired pattern, developed for about two minutes in Kodak Micro ~o Re~istTM developer, rinsed for 15 seconds in Kodak Micro ResistTM rinse, and then etched in a solution of 400 g/l of FeC13-6H20 to give an array of ralsed squares of 300 ~m edge length. ~ach 3quare touched the corner o~ th~ next ~quare along one diagonal of the array, and wa~ laterally s~paratcd from the adjacent raised square along the orthogonal axes o~ the array by 600 ~m. The embos~ed copper ~heet was fixed in con~act ~ith a curved aluminum heating block, radius 7 cm, and the block was 0 maintained at 165C.
A dye-receiver was prepared by coating a glass plate with a thin layer of Geon 427TM (B. F.
Goodrich Company~ vinyl chloride:vinyl acetate copolymer (86:14). The solution was poured onto the glass plate, ~pread evenly, and then the ~urplus poured off. The resulting thin layer was allowed to dry, giving a clear, dry film o~ about 3 ~m thick.

A ~ilter array of cyan, magenta and yellow dyes was prepared by succe~sively placing the cyan, magenta and yellow portions of the dye-donor described above in contact with the gla~s plate and rolling the plate and dye-donor element acroz~ the heated embosæed roller at a speed of about 5mm per second.
It was seen that the raised portions of the roller caused squares of dye of approximately 300 ~m edge length to transfer to the coated glass plate, forming an array of cyan, magenta and yellow squares. The dyes were then driven deeper into the receiving layer by an overall heating step.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifica~ions can be effec~ed within the spirit and scope of the invention.

Claims

1. A method of making an array of a repeating mosaic pattern of colorants carried on a support using (a) a plurality of donor materials each comprising respectively a sublimable dye of a different color, and (b) a receiver element comprising a support having thereon a dye-receiving layer, wherein each donor material is in turn brought into face-to-face contact with the receiver and heated patternwise by contact with a heated embossed surface to transfer the desired pattern of dye to the receiver layer.

2. The method of Claim 1 in which the receiver layer comprises silica or a polymeric layer

3. The method of Claim 1 in which there are three donor materials which provide the mosaic pattern in the additive primary colors red, green and blue.

4. The method of Claim 1 in which the embossed surface is of brass or copper.

5. The method of Claim 4 in which the embossed surface is formed by etching a brass or copper sheet bearing a patterned resist image.

6. The method of Claim 1 in which the embossed surface is mounted on a heated roller.

7. The method of Claim 1 in which the heated embossed surface is applied to the back of the donor material while it is in contact with the receiver element.